1. Field of the Invention
The subject invention pertains to the control of gyroscopes and particularly to the control of a directional gyroscope employed in a gyro compass system which also includes an azimuth reference preferably a flux valve of conventional structure. Specifically the invention pertains to an improved, more reliable, more compact and less costly start-up conditioning means operable under all initial orientation conditions of the gyroscope to quickly orient the gyro with the azimuth reference while the rotor component of the gyro is spun to a predetermined speed.
2. Description of the Prior Art
The subject invention is an improvement of the apparatus disclosed in U.S. Pat. No. 3,324,731 entitled "Start-Up Conditioning Means For An Azimuth Reference", issued June 13, 1967 in the names of W. Burmeister, B. Duckworth and R. Radtke and assigned to the same assignee as the subject application. In this prior art apparatus, a synchro is coupled between a flux valve and a directional gyro. The synchro rotor produces an electrical output signal; the sense and magnitude of which depends upon the sense and magnitude of the angular displacement between the directional gyro and the flux valve, i.e., the signal is proportional to the synchronization error between the gyro and the flux valve.
Synchronization of the directional gyro to the flux valve is accomplished by a torque exerting means which exerts a greater than normal torque about the horizontal axis of the gyro to precess the vertical ring about the vertical axis in such a direction that the gyro is synchronized to the flux valve under start-up conditions and maintains synchronization at a normal torquing energy level at a time subsequent to the start-up operation.
Initially, when the prior art apparatus is energized and the gyro rotor is being brought up to normal speed, if the synchronization error signal produced in the winding of the rotor is of one sense, a first relay is energized which couples high level electrical energy from source into a first set of windings that produce rotation in the torque exerting means in a direction to reduce the error signal. Alternatively, if the synchronization error signal is of an opposite sense, it is coupled to a second relay which is energized and couples the high level energy into a second set of windings on the torque exerting means that will produce rotation in an opposite direction to that produced by energizing the first set of windings.
The high level energy is applied to the torque exerting means until the vertical ring of the gyro is precessed a sufficient amount about its axis to bring the directional gyro into synchronization with the flux valve. At this instant the first and second relays are de-energized thereby closing a circuit between the source and a threshold detector. When the speed of the gyro rotor reaches a predetermined level below its normal operating speed, the threshold detector senses the speed of the rotor and completes a circuit from the source through contacts of the first and second relays to the coil of a third relay. Upon energization of the third relay by the output of the threshold detector, the synchronization error signal is coupled through corresponding contacts on the three relays to the corresponding set of coils in the torque exerting means. As a result, any further synchronization error produces an output electrical signal at a normal energy level which is coupled through the contacts of the three relays to the corresponding set of coils on the torque exerting means. Thus the gyro is precessed at a normal energy level during normal operations.
The three relays of the prior art device are large contactor type relays having high power ratings as required to switch the high level energy to the respective set of torquing coils. Therefore, these relays occupy a substantial volume which requires mounting in a separate container outside the gyro casing. Also, the high power requirements reduce reliability due to temperature rise. It will be readily appreciated that for aircraft applications the large relays are very undesirable because of their questionable reliability, added weight, excessive volume and high cost. Also, such large relays are subject to acceleration forces which in aircraft applications may cause intermittent and undesirable closure or opening thereof during aircraft maneuvers and/or vibrations. The invention disclosed in the subject application employs discrete electronic components and sub-miniature relays which provide a significant reduction in volume, weight and overall system cost because this combination of components can be easily packaged within the gyro casing or housing thereby eliminating a separate electronics housing.
Additionally, in the prior systems it is possible for the gyros rotor and gimbal to have previously come to rest with the flux valve synchro on the gyro oriented at an ambiguous null, i.e., 180.degree. from the normal null position. Therefore, at turn-on, the prior art apparatus may not cause this misalignment and may synchronize the gyro to the flux valve at a displacement of 180.degree.. The invention described herein provides a means operable at turn-on which assures that the system will not synchronize at a false null.